Telescope

Telescopes are used by Astronomers and students alike for observation of planets, stars along with galaxies. Astronomical telescopes help the observation of astronomers by collecting more light than a normal eye. Basically a telescope magnifies distant objects.

These days Telescopes are coming in a lot shapes and sizes. Let's understand the way a Telescope works.

Working of a Telescope
To understand the working of the Telescope let's put a simple question why we can't see what is a written in a a coin beyond a certain distance. The answer is very simple. The object in this case coin, is not able to take much space on the retina (the eye's screen) . Perhaps if one had bigger eyes with which more light could have been collected for creation of a brighter picture. Then a part of this image could have been magnified so that it could stretch out with more pixels to the retina. Now coming to the Telescopes, for making distant objects nearer, two pieces are very important.

The objective lens as in a refractor telescope or the primary mirror in a reflector telescope is able to collect considerable amount of light from distant objects. Consequently the light, or image, is then brought to a point or focus. The second crucial piece of equipment is an eyepiece lens. The eyepiece lens takes the bright light from the focus of an objective lens or the primary mirror as the case may be. They then spread this light out magnifies it. As a result taking up a considerable portion of the retina. This is something similar to the working of a magnifying glass.


So to summarise a telescope is a combination of the objective lens or primary mirror with an eyepiece. The primary idea behind a telescope is collection of light, a lot of that and then forming a bright image inside the telescope. A device like a magnifying glass is then used to to magnify (enlarge) that bright image for garnering a considerable space on the retina.

The image below shows the design of a simple Telescope. A big lens gathers the light and directs it to a focal point and a small lens brings the image to your eye.

Components of a Telescope

Parts of the Telescope Parts of the equatorial mount Dew Cap Azimuth Adjustment Tube Rings Latitude Scale Focuser Polar Alignment Scope Star Diagonal Declination Circle Equatorial Mount Counterweight Bar Counterweight Right Ascension Axis Lock Accessory Tray Right Ascension Hour Circle Finderscope Declination Slow Motion Control Knob Eyepiece Right Ascension Slow Motion Control Knob Optical Tube Tube ring

Five basic questions to ask before buying a Telescope : Why are you purchasing a Telescope? What is your budget? What you intend to do with the Telescope ? How dark is the sky? What is the seriousness level of Astronomy?

Selection of a Telescope
Choosing the right kind of Telescopes is a challenging task in itself. Some of the broad points to be kept in mind are enumerated here.

» Power configuration can be dicey in a Telescope : To give a very clear illustration, let's say you encounter a Telescope with "650x" or for that matter any other reference to power that is displayed prominently. Then just ignore its just a marketing gimmick. Even the choicest of the Telescopes are restricted to approximately about 50x-75x per inch (25.4mm) of the aperture. So the advice is do not purchase a Telescope based on the power. With a 32x magnification you can observe Jupiter along with its moons, Saturn and its rings etc.

» Aperture of a Telescope : A mirror or lens's diameter is considered as one of the most crucial attribute of a Telescope. Within a price tag the idea would be to buy as much aperture as one could. Though large aperture refractors (lens based) is a bit on the expensive side. That is the reason why a mirror based Telescope is often the viable option.

» Good solid Mounting Design : A solid mount is always necessary for a smooth star gazing. Say for example if the mount is difficult to use, wobbly then having the best optics would not be of much use. What you need would be a perfect combination of solid and simple to use mount and an aperture.

» Eye piece : Some of the things to consider in eyepieces are the following:

• Consider apparent field of view with true field of view
• Another important thing to consider is the diameter of the eyepieces. A standard 32mm barrel is an industry standard and can fit most Telescopes having a 100 mm aperture or more.

» Consider the option of used Telescopes : It is often found that there is absolutely no need to go for the latest models of a Telescope. Infact a lot of money can be saved by selecting older model Telescopes.

» Reflector Telescope vs Refractor Telescope : Whether to go for Refractor Telescope or a Reflector Telescope depends on a lot of factors. If you are a beginner, and want to get as much aperture as possible for the amount spent then a reflector telescope (mirror based) is a good option. For procuring refractor telescope (lens based) reasoning may be a bit complex. Inexpensive Refractors that are less costly face problems with false color, but offer better compactness. When used in daylight conditions Refracting telescope offer more pleasing views. As compared to Refractors most Reflecting telescopes are generally large but offer better capacity to gather light.

Types of Telescope
Reflector Telescope
Reflector Telescopes are best for the students and beginners alike to get familiar with the different facets of astronomy. A Reflector Telescope uses a curved primary mirror to gather and focus light and unlike a Refractor Telescope color distortion is never endured by them.

Refractor Telescope
The refractor telescope is essentially dioptric telescope typically employing lenses for light gathering and focusing. Infact the initial Telescopes that were built was only of the refractor type.

Catadioptric Telescope
Catadioptric Telescope typically use a combination of both lenses as well as mirrors for bringing light to focus.

Terrestrial Telescope
Mostly Terrestrial Telescopes are prismatic. They follow the primary design of a large monocular and can be applied with a range of different eyepieces. Typically Terrestrial Telescopes feature an Optical system for erecting the image. Though offering many spectacular features but Terrestrial Telescopes are very costly.

Dobsonian Telescope
A dobsonian telescope is basically a type of reflecting telescope. That is, it uses a mirror and not a lens. It has more or less an identical design as a newtonian telescope. The name Dobsonian, derived from the design of the mount structure made popular by John Dobson. Typical features of Dobsonian Telescope include low cost, large aperture, rugged and a very simple design.